This invention relates to an optical scanning device for providing a compact copier with the ability to reproduce original documents at a relatively high copy rate. More particularly, the invention relates to improvements in the drive mechanism which moves a reciprocable carriage supporting the scanning optical components.
In the copying art, it has been found advantageous to support the original to be reproduced upon a stationary viewing platen while recording an image of the original upon a photosensitive plate. Copies of the original can then be conveniently reproduced from the plate. It has also been desirable to provide means for compacting a copying device while still maintaining a high fidelity reproduction of the original. In these devices, the optical system used to scan the original must be vertically compressed in order to achieve the required compact dimensions. An exemplary example of such a system is disclosed in U.S. Pat. No. 3,832,057. In the optical scanning arrangement disclosed thereon, a stationary viewing platen is arranged to support an original to be copied within a substantially horizontal plane. Scanning optical elements on a carriage are swept horizontally across the platen from one margin thereof to the opposite margin at a constant velocity to scan successive incremental areas of the original. Additional optical elements are disclosed to maintain the required constant conjugate length between the object plane of the system and the stationary lens disclosed therein.
While systems of the type disclosed above can produce satisfactory copy quality at relatively slow copy speeds, attempts to increase copy speed above a certain point (approximately 26 cpm) result in lead edge "skips" on the copy paper. Because of the location of the various components, the carriage mass is unequally distributed, and excessive changes of speed of the carriage, i. e. carriage deceleration from an end of scan followed by rapid acceleration at a start of scan position; create an inertial moment of force (torque) acting on the carriage. This force tends to cause the carriage to oscillate from side to side as the scanning cycle begins, the oscillation continuing until the energy is absorbed by the system. This results in blurring of the lead edge of the document being scanned.